1. Field of the Invention
This invention relates to an improvement in a method and apparatus for vacuum alehydrating a colloidal substance such as neat soap, glycerin, or varied fats and oils, and cooling and releasing a gas resulting from the vacuum dehydration.
2. Description of the Related Art
FIGS. 4 and 5 show a conventional method and apparatus of this type for treating a colloidal substance.
In the vacuum drying apparatus, as shown in FIG. 4, a colloidal substance to be treated is taken from a raw material supplying device 1, and supplied to a vacuum drying tower 2 after being heated through a heat exchange with heating vapor. The substance is injected into a vacuum chamber 9 to be dehydrated under saturated vapor pressure. The dehydrated substance is transferred from a bottom of the vacuum chamber 9 to a substance extractor 3 for kneading and discharging the substance. A gas discharged from the vacuum drying tower 2 is cooled in a cooling device 4 by cooling water supplied from a cooling tower 4A. As shown in FIG. 5, the cooling device 4 comprises a raindrop type barometric condenser for forming water screens across a gas passage therein. The discharged gas is forced to contact the cold water to be cooled.
The prior art noted above has the following drawbacks.
In view of the relationship of saturated vacuum to temperature, the water acting as a refrigerant in the cooling process should be as cold as possible to secure a high degree of vacuum. Thus, the water used is recirculated while being cooled. However, the recirculating water carries fine particles of soup captured through contact, and becomes turbid and foamy. In addition, a large quantity of soap particles adhere to the cooling tower to lower its cooling effect. Consequently, part of the recirculating water must constantly be withdrawn from the recirculating system, with replenish water constantly introduced into the recirculating system to compensate for the withdrawn part of water. This is uneconomical in that a large quantity of water is used.
The cooling tower has the advantage of allowing impurities to mix into the water to some extent. However, a temperature difference between inlet and outlet of the cooling tower can be set to only about 5.degree. C. to maintain its function. In summer when the water temperature may rise to about 30.degree. C., the function to cool the discharged gas could deteriorate to lower the degree of vacuum, thereby adversely influencing the drying treatment.
Moreover, the barometric condenser must be installed at a height at least 11 meters over a liquid surface of a water seal tank in order to maintain the degree of vacuum. Consequently, the entire apparatus tends to be large, and involves difficulties of maintenance operations to be carried out at high locations.
A vacuum pump used as a suction device must draw air contained in the water used in the barometric condenser as well as the gas resulting from the dehydration in the vacuum drying tower. This requires the vacuum pump to have a large displacement.